Constitutive modeling of pressure dependent plasticity and fracture in solder joints

Kotas

Khatibi

et al. 2018

KEM

The adhesive strength of ceramic - copper interfaces was measured in four point bending using a central notch for crack initiation. According to our method, plastic deformation may occur during the delamination process. FEM simulations were employed in order to separate elastic and plastic contributions to the energy consumption of the experiment. In conclusion, a novel delamination criterion based on the stress intensity at the crack tip was established. Here, the stress invariant J3is used as indicator for delamination of the interface. Agreement between experiments and theoretical interpretation is demonstrated for copper layers directly bonded to aluminum oxide.

Section: Fem Simulation and Theoretical Interpretationmentioning

confidence: 99%

Characterization of Adhesion Properties by Delamination of Ceramic-Metal Interfaces in Four Point Bending

Kotas

Khatibi

et al. 2018

KEM

“…From the phenomenological point of view, the justification for this step is simply that the numerical fits to experiments are improved. But there are also some theoretical aspects behind this idea: When the crystal lattice is stretched, the dislocations have more space to move and therefore the resistance to glide is reduced [10]. On the other hand, when the material is under pressure P, the opposite is observed.…”

Section: Assumptions Of Our Dislocation Modelmentioning

confidence: 99%

Constitutive modelling of copper films on silicon substrate

2015 16th International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and

Zarbakhsh

2015

Self Cite

In order to characterize the material behavior of copper films deposited on silicon substrate, wafer curvature experiments were performed. The samples were exposed to repeated cycles in the range between -50°C to 400°C. The diagrams of film stress versus temperature show linear film behavior followed by plastic flow. Tn fact, a pronounced Bauschinger effect was observed which is attributed to back-stress arising from the dislocation structure in copper films. For better understanding of the underlying mechanisms, a new statistical dislocation model was developed which can nicely be fitted to experiments. However, the algorithm of the dislocation model appeared to be very time consuming during computation. Therefore, a second model was developed which can refit the experimental data with high accuracy using a fast algorithm. We call this model pressure dependent combined isotropic and kinematic hardening. This model was implemented in ANSYS with user-subroutine usermat.978-1-4799-9950-7/15/$31,00 ©2015 IEEE -1 / 7 -

“…The cross contraction of the solder is obstructed by the vicinity to the stronger copper base material. Therefore, the tensile strength of thin solder joints is higher than that of thicker joints [1].…”

Section: Introductionmentioning

confidence: 97%

On the Influence of Internal Void Size on the Fracture Stress of Constrained Solder Joints

Khatibi

Magnien

2016

SSP

The fracture strengths of thin solder joints were investigated experimentally and with Finite Element Analysis. Due to a constraining effect, thin solder joints can carry loads which are much higher than the ultimate tensile strength of bulk solder material. On the other hand, thin solder joints show a tendency of being brittle. In fact, the tensile properties show a dependence on the quality of the intermetallic compound at the interface to the base material. Consequently, the size of microscopic defects in the intermetallic compound has a dominant influence on the fracture stress. This behavior could nicely be explained with Finite Element simulations based on strain gradient elasticity.